Electronic circuit assemblies which include a plurality of different electronic components mounted together on modules, often called a circuit boards, are common in computer and other electronic equipment. The boards are usually formed of a fiberglass-filled composition. Each of the electronic components on a board has leads which are electrically interconnected to leads on other components by conductors directly formed on the board.
In conventional assemblies of this type, the electronic components are mounted on one surface of the board, and the leads of the components pass through plated holes to the opposite surface of the board where they are soldered, to thereby secure the components to the board, as well as make the required electrical connections. Surface mount technology (SMT) boards differ from conventional boards in that the component leads are soldered to conductive "pads" disposed on the surface to which the particular component is to be mounted. The leads, therefore, need not, and generally do not, pass through holes to the opposite surface of the board. This surface-mount technology is finding increasing usage in the manufacture of circuit board assemblies, because it has marked advantages over prior conventional technology. Specifically, the procedures for producing SMT board assemblies are generally simpler and more economical than the procedures to fabricate conventional board assemblies.
Further, SMT board assemblies permit reductions in the sizings of the individual components mounted on the boards and reductions in the sizes of the boards as well. They also permit the unrestricted mounting of components on both surfaces of the boards, thus providing denser assemblies, i.e. with increased circuitry disposed in less space.
In a typical SMT board repair apparatus, a component to be removed is heated by a hand-held hot air blower to a temperature such that the solder, which joins the leads of the component to the SMT board at solder pads on the board, melts. The component is then removed. In like fashion, components are added to SMT board assemblies by placing the leads, which have a solder paste applied thereto, on the pads of the SMT board and then applying a directed hot air flow over the component and the leads such that the solder paste is liquidified. Renewal of the heat source then permits the solder to solidify and thereby secure the component to the board.
An alternative repair method involves the use of a hand-held soldering iron, which functions much like a pair of tweezers. The tips of the iron, when squeezed together, have a shape matching the perimeter of the component to be removed from the SMT board. The tips of the iron are positioned on the leads of the component to be removed and the iron is heated until the operator observes the solder melting sufficiently to permit the component to be removed from the board. For installing components on the SMT board, this procedure is reversed.
Both of the above-referenced methods of repair are slow and tedious, and require a significant amount of manual dexterity in their applications. The application of heat necessary to melt the solder can result in damage to the SMT board itself, and the conductors found thereon, in the form of buckling or even delamination. The use of hot air circulation over the board also causes, in some instances, electrostatic discharge damage to components positioned on the board, due to the presence of ions in the heated air.
In light of the above, it is an object of this invention to provide an improved apparatus and method for the repair of surface-mount-technology circuit board assemblies. Another object of this invention is to provide an SMT circuit board repair apparatus which is semi-automatic and requires little operator training and only routine operator involvement.
Still another object of the invention is to provide an SMT circuit board repair apparatus and method which minimizes the likelihood of damage to the board and to the components on the board.
Other objects will be specified in or obvious from the detailed description of the illustrated embodiments of the invention which follows.